Pulse integrating circuits



PULSE INTEGRATING CIRCAUITS l Filed NOV. 16, 1945 MQW ATTORNEY Patented June 21, 1949 UNITED STATES PATENT OFFICE PULSE INTEGRATING CIRCUITS James R. Day, Peconic, N. Y., assigner to Radio Corporation of America, a corporation of Dela- Application November 16, 1945, Serial No. 629,169

(Cl. Z50-27) Claims. 1

This invention relates to pulse integrating circuits, such as are used to count pulses.

An object of the invention is to provide an improved circuit for generating a step wave voltage having a plurality of steps or risers corresponding in number to a desired number of applied input waves.

The integrating circuit of the invention has been found to be especially useful at the receiving terminal of a pulse type multiplex communication system for generating a step wave whose diierent steps or risers, by virtue of their different amplitudes, control different channel selectors. In such multiplex systems, it is customary to transmit short duration pulses of radio frequency energy at constant amplitude and at a iixed average repetition rate. The pulses in the different channels are transmitted consecutively and have their occurrence time or phase modulated within predetermined limits. During each cycle of operation or synchronization period, there are transmitted pulses from all of the channels followed by a synchronizing pulse of longer duration than the channel pulses. This cycle of operation repeats itself continuously at the synchronization period. One such system is described in copending application Serial No. 608,957, iled by W. D. Houghton on August 4, 1945. At the receiving terminal of such a pulse multiplex system it becomes necessary to selectively control or render operative the different channel apparatus (selectors) at the proper phase relative to the incoming pulses. For this purpose, a new step wave voltage is generated at the receiving terminal.

In the drawing:

Fig. l illustrates a circuit for generating a step wave voltage, in accordance with the principles of the invention, and

Figs. 2a and 2b illustrate a series of curves representing voltage variations at two designated points in the circuit of Fig. l.

Referring to Fig. 1 in more detail, there is shown a plurality of vacuum tube electrode structures A, B, C, D, E, F and G. The anodes of tubes A, B, C and G are connected to a common source of anode polarizing potential +B which is the positive terminal of a source of unidirectional potential. By way of example, +B may be +300 volts relative to ground. Although these electrode structures are illustrated within individual evacuated envelopes, it should be understood that, if desired, two of these can be located within a single envelope to form a, dual-triode tube. For example, electrode structures B and C can form a single tube and electrode structures E and F can form another single tube.

Triode vacuum tube C is biased by the resistorcondenser combination 8, 9 in its cathode circuit so as to be normally non-conducting. The grid of triode C is connected through a resistor I0 and a coupling condenser Il to lead I2 extending to a source of periodically recurring direct current input pulses of positive polarity. Each of these input pulses is of suflicient magnitude to overcome the cut-off bias of tube C and cause it to conduct for the duration of the applied pulse. Putting it in other words, no anode current flows in tube C in the absence of input pulses to its grid.

A storage or step condenser 1 is connected between ground and point Y in the cathode circuit of tube C via lead 6, as a result of which an incremental charge of voltage is built up on this condenser whenever tube C conducts. A step wave voltage is built up across condenser 1, and this step wave voltage has a plurality of steps of increasing amplitude corresponding in number to a desired number of input pulses.

Tube B is a normally non-conductive tube which, when it conducts, serves to restore coupling condenser Il to its original condition after each input pulse or, stated otherwise, it recharges condenser Il after each input pulse and before the next succeeding input pulse. This tube may loosely be called a snubberl The cathode of tube B is connected to the grid of tube C, while the grid of tube B is connected via lead 5 to point Y.

Tube G is a cathode follower which couples the step wave generator to a suitable load circuit connected to lead 4 and connected to the cathode of this tube. Tube G may be called a step Wave output tube and is used to supply high current for the load circuit from the step Wave generator. Within the region of linear operation of this tube, the cathode voltage "follows the grid voltage. There is no grid current in tube G when it is operated properly. The iiow of anode current through the tube causes a voltage drop in the resistor connecting the cathode to ground.

Tubes D, E and F are normally non-conductive discharge tubes which become conductive simultaneously. The grids of these tubes are connected together and their cathodes are also connected together and to ground.

Tube E has its anode connected to point Y in the cathode circuit of tube C. It should be noted that the space vpath of this tube is effectively across step condenser 1. When this tube is caused 3 to conduct, it forms a low impedance discharge path across condenser 1.

Tube F, when it conducts, insures the quick discharge of the load capacity connected to lead il and the cathode of tube G. Putting it in other words, discharge tube F prevents a gradual trailing edge on the output step wavejwh'ichwouldl otherwise occur due to: the capacity loading on the cathode of tube G.

Tube D has its anode connected via lead 3 to the junction point of coupling condenser I`I vand resistor l both of which are in the grid circuit of tube C. This tube D prevents tube C from conducting during the discharge Vof, step condenser '1. The reason for this is as' follows: When discharge tube E conducts to discharge step con-` denser 1, the cathode voltage of tube C is lowered (made negative) which is equivalent to' raising the grid of tube C in a positive direction. If, at this'time; tube C is permitted t o conduct, it would produce a counteracting effect making it impossible to achieve the desired discharge of step condenser 'l at the end of thestep wave. To avoid this counteracting effect, tube v D is caused to conduct at the same time as tube E, as a result of whichthe voltage on the grid of tube C` is lowered simultaneously withl and to substantially the same extent as the voltage on the cathode of tube Cis lowered. Hence, tube C remains yin its cut-olf or non-conductive condition during the time of discharge of step condenser l.

Tube A is a cathode follower which provides a low impedance drive for the discharge tubes D, E and F from a higher impedance synchronizing circuit. A synchronizing pulse of positive polarity is supplied to the grid of tube A via lead 2 for each synchronizing period. The grid of this tube is connected via a grid bias resistor to a source of negative direct current potential +C; and to the cathode of the tube. The bias on the grid is sufficient to prevent anode current from flowing in the tube in the absence of a synchronizing pulse. This synchronizing pulse occurs once 'during each cycle of operation, after the channel pulses, and is of such magnitude as to cause tube A to conduct suddenly. The synchronizing pulses recur at intervals materially shorter than ,the RC grid circuit time constant of tube A. When tube A conducts, it supplies a positive pulse of voltage to the grids of discharge tubes D', E 'and F and causes these discharge tubes to conduct simultaneously.

A description `of the operation of Fig. l will now be given. Let it be assumed, for example, that it is desired to generate a stepvwave voltage having nine steps or risers for use in the receiv; ing terminal of an eight channel pulse multiplex system for selectively and sequentially rendering operative the different channel selectors. This number of risers is givenby way of illustrationJ only, because the invention was actually embodied in such an eight channel pulse multiplex system which utilized a synchronizing pulse (for each synchronizing period) of longer duration than the channel pulses... Let it also be assumed that 90 kc. constant amplitude and constant frequency inputpulses of positive polarity are supplied to lead |22.

Tube C will be caused to conduct by the positive going fronts (leading edges) of the input pulses,A and will be cut off between ypulses by the Seli-bias .developed @0295s Condenser. 91e its cathode circuith `When tube conductson these positive going fronts of the input-, pulses, itactfs as a resistance from +B to' 'condenser 1. ach

time tube C conducts, there is built up on condenser l an incremental charge of positive' polarity of an amplitude corresponding to a rise or step in the complete step wave. This charge on condenser l cannot leak cif. During most of the negative going portions (trailing edges) of the kc. input pulses; tube C will be cut-off (i. e., non-conducting).

when the voltage on the grid of tube C is lowered by the negative going portions of the 9i) lic. input pulses, the voltage on cathode of tube B is also lowered, as a result of which tube B will conduct and supply the necessary charging current for condenser l! (via the space current path of tube B and its connection to +B) to restore condenser H to its normal condition.

Because the increments of charge on step condenser 'I do not leak off between input pulses, there is developed a step'wave voltage across this condenser. This step wave voltage is coupled to the load through cathode follower G. At the end of each synchronization period corresponding to a predetermined time interval microseconds, for example), the step wave is discharged by virtue ofv a synchronizing pulse supplied to tube A causing the discharge tubes D, E and F to conduct. The length or duration of this synchronizing is longer than the input pulses and assures a desired discharge of the step wave.-`

By way of example, the synchronizing pulse may have a duration of 3 microseconds, while the 90 kc. input pulses may each have a duration of one microsecond or less.

Fig. 2a illustrates the appearance of the voltage at the grid of tube C, While Fig. 2b illustrates the appearance of the step wave output Voltage available at the cathode of tube G, as seen on an oscilloscope. The slight pips on the front edges of the steps or yrisers of the voltage wave of Fig. 2a are second order effects.

The amplitude of the step in the step wave can be varied by varying resistor 8 which controls the' average conducting resistance of tube C and hence the value of the charge increments built up on step condenser 1.

Anv advantage of the step wave generator of the invention is that it does not require the use of pulse transformers. Such pulse transformers are used in some known pulse integrating circuits and are a disadvantage, particularly when variable length pulses are utilized.

The term ground used in the specification and appended claims is not limited to an earthed connection but is deemed to include any point or surface of zero potential for direct current or alternating current.

What is claimed is:

1. A pulse Aintegrating circuit comprising a vacuum tube having an anode, a cathode and a control electrode, a source of 'anode potential connected to said ano'de means for normally biasing said tube to cut-off, an input circuit including in series therewith a capacitor coupled t'o 'said control electrode for supplying pulses thereto of such polarity and magnitude as vto cause said tube to conduct for substantially the duration of each pulse, a condenser connected between the cathode of said tube and ground, whereby an incremental increase in voltage `is built up on said condenser for each input pulse during a cycle of operation, a space discharge pathk across said condenser, another normally non-conductive rspace discharge .path connected between the grid side of said input circuit capacitor and grnd, and 'means 'for simultaneously making both of said discharge paths conductive after a predetermined number of input pulses.

2. A lpulse integrating circuit comprising a first vacuum tube having grid, anode and cathode electrodes, means for normally biasing said tube to the anode current cut-off condition, an input circuit including in series therewith a capacitor and a resistor coupled to said grid for supplying recurring pulses thereto of such magnitude and polarity as to cause said tube to conduct for substantially the duration of each pulse, a condenser connected between the cathode of said tube and ground, whereby an incremental increase in voltage is built up on said condenser for each input pulse during a cycle of operation, a second vacuum tube having a grid, anode and cathode, a connection from the cathode of said last tube to the grid of said iirst tube, a connection from the grid of said second tube to the cathode of said rst tube, a source of anode polarizing potential connected to the anodes of both tubes, a normally non-conducting space discharge path connected across said condenser, and means for causing said space discharge path to become conductive after a predetermined number of input pulses.

3. A pulse integrating circuit comprising a rst vacuum tube having grid, anode and cathode electrodes, means for normally biasing said tube to the anode current cut-off condition, an input circuit including in series therewith a capacitor and a resistor coupled to said grid for supplying recurring pulses thereto of such magnitude and polarity as to cause said tube to conduct for substantially the duration of each pulse, a condenser connected between the cathode of said tube and ground, whereby an incremental increase in voltage is built up on said condenser for each input during a cycle of operation, a second vacuum tube having a grid, anode and cathode, a connection from the cathode of said last tube to the grid of said first tube, a connection from the grid of said second tube to the cathode of said iirst4 tube, a source of anode polarizing potential connected to the anodes of both tubes, a normally non-conductive space discharge path connected across said condenser, another normally nonconductive space discharge path connected between ground and the junction point of the capacitor and resistor of the input circuit, and means for simultaneously causing both of said discharge paths to become conductive after a predetermined number of input pulses.

4. A pulse integrating circuit comprising a vacuum tube having an anode, a cathode and a control electrode, a s-ource of unidirectional potential having its 'positive terminal connected to said anode means for normally biasing said tube to cut-off, an input circuit including in series therewith a capacitor coupled to said control electrode for supplying pulses thereto of such polarity and magnitude as to cause said tube to conduct for substantially the duration of each pulse, a condenser connected between the cathode of said tube and ground, whereby an incremental increase in voltage is built up on said condenser for each input pulse during a cycle of operation, a normally non-conductive space discharge path across said condenser, another normally non-conductive space discharge path connected between the grid side of said input circuit capacitor and ground, means including a normally non-conductive electron discharge device operative at a frequency which is .a submultiple of the frequency of the input pulses for causing both of said space discharge devices to become simultaneously conductive, and a connection for deriving from said condenser a step wave voltage having a plurality of steps or risers.

5. A ypulse integrating circuit comprising a first vacuum tube having grid, anode and cathode electrodes, a self-bias condenser-parallel resistor combination having one terminal connected to said cathode and another terminal connected to ground via a storage condenser, said combination normally biasing said tube to the anode current cut-off condition, a lead for supplying recurring input pulses of positive polarity to said grid through a capacitor, said pulses having sufficient magnitude to cause said tube to conduct for at least a portion of each input pulse, whereby an incremental charge is built up on said storage condenser each time said tube conducts during a cycle of operation, a second vacuum tube having grid, anode and cathode electrodes, a direct connection between the cathode of said sec-ond tube and the grid of the rst tube, `a direct connec- -tion between the grid of the second tube and said last terminal of the condenser-parallel resistor combination, a source of anode polarizing potential connected to the anodes of both tubes, means for discharging said storage condenser at a frequency lower than the repetition rate of said recurring input pulses, and a connection for deriving from said storage condenser the overall voltage built up thereon between discharges.

6. A pulse integrating circuit comprising a i'lrst vacuum tube having grid, anode and cathode electrodes, a self-bias condenser-parallel resistor combination having one terminal connected to said cathode and another terminal connected to ground via a storage condenser, said combination normally biasing said tube to the anode current cut-oil condition, a lead for supplying recurring input pulses of positive polarity to said grid through a capacitor and a resistor in series, said resistor being nearest said grid, said pulses having suiiicient magnitude to cause said tube to conduct for at least a portion of each input pulse, whereby an incremental charge is built upon said storage condenser each time said tube conducts during a cycle of operation, a second vacuum tube having grid, anode and cathode electrodes, a direct connection between the cathode of said second tube and the grid of the first tube, a direct connection between the grid of the second tube and said last terminal of the condenser-parallel resistor combination, a source of anode polarizing potential connected to the anodes of both tubes, a pair of normally non-conductive vacuum tube electrode structures having their grids directly connected together and their cathodes connected to ground, a connection from the anode or one tube structure of said pair to the junction point of the series connected capacitor and resistor, a connection from the anode of the other tube structure of said pair to the cathode connected side of said storage condenser, whereby said last tube structure of said pair constitutes a discharge path for said storage condenser, means coupled to both grids of said pair of tube structures for supplying to them pulses of such amplitude as to cause them to conduct suddenly and at a repetition rate lower than the repetition rate of said recurring input pulses, a cathode follower tube coupled to said storage condenser for deriving therefrom a voltage wave representative of the charges built up on said storage condenser 'Z between discharges, `and a load circuit coupled to the cathode of said cathode follower tube.

7. A pulse integrating circuit comprising a vacuum tube lhaving a cathode and a control electrode, a source of power supply coupled to said tube, means for normally biasing said tube to cut-off, an input circuit including in series therewith a capacitor coupled to said control electrode for supplying pulses thereto of such polarity and magnitude as to cause said tube to conduct for substantially the duration of each pulse, a condenser connected between the cathode of said tube and ground, whereby an incremental increase in voltage is built up on said condenser for each input pulse during a cycle of operation, a space discharge path across said condenser, another space discharge path connected between the grid side of said input circuit capacitor and ground, a cathode follower tube having a grid connected to that side of said condenser which is connected to the cathode of said vacuum tube, a resistor connected between the cathode of said follower tube and ground, a space discharge path across said last resistor and means for simultaneously causing all three of said space discharge paths to become conductive simultaneously after a predetermined number of input pulses.

8. A pulse integrating circuit comprising a rst vacuum tube having grid, anode and cathode electrodes, means for normally biasing said tube to the anode current cut-off condition, an input circuit including in series therewith a capacitor and a resistor coupled to said grid for supplying recurring pulses thereto of such magnitude and polarity as to cause said tube to conduct for substantially the duration of each pulse, a condenser connected between the cathode of said tube and ground, whereby an incremental increase in voltage is built up on said condenser for each input pulse during a cycle of operation, a second vacuum tube having a grid, anode and cathode, a connection from the cathode of said last tube to the grid of said first tube, a connection from the grid of said second tube to the cathode of said rst tube, a source of anode polarizing potential connected to theanodes of both tubes, a normally non-conductive space discharge path connected across said condenser, another normally non-conductive space discharge path connected between ground and the junction point of the capacitor and resistor vof the input circuit, a cathode follower tube having a grid connected to that side of said condenser which Vis connected to the cathode of said vacuum tube, aV resistor vconnected between the cathode of said follower tube and ground, a space discharge path acrosssaid last resistor, and means for simultaneously causing Aall three of said space discharge paths to become conductive simultaneously after a predetermined number of input pulses.

9. In a pulse counter circuit, a lcharge collecting condenser, means including an electronic circuit for applying incremental charges to said condenser in response to a corresponding number of applied pulses, a cathode follower tube having a grid connected to one plate of said condenser and a cathode connected through a resistor to the other plate of said condenser, a space discharge path across said resistor, means operative after a predetermined number of input pulses greater than two for rendering said space discharge path conductive, and an output lead connected to the cathode of said follower tube for deriving a sten wave voltage from said counter circuit.

10. In a pulse counter circuit, a cathode fol lower tube having a cathode resistor, an output circuit coupled'to said cathode resistor, a space discharge path across said resistor, and means operative after a predetermined number of input pulses greater than two for rendering said space discharge path conductive.

JAMES R. DAY.

REFERENCES CITED UNITED STATES PATENTS Name Date Page Mar. 10, 1.942

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